Day 2

Advent of Code: Worked Solutions

Setup

Import libraries:

library(tidyverse)
library(unglue)

Read text input from file into a set of start/end values:

input <- read_lines("../input/day02.txt") |> 
  str_split_1(",") |> 
  unglue_data("{start}-{end}", convert = TRUE)

Part 1

Use regex to match all instances of single-repeated substrings within the range of integers:

input |> 
  with(map2(start, end, seq)) |> 
  unlist() |> 
  keep(\(x) str_detect(x, "^(.+)\\1$")) |> 
  sum()

Part 2

Alter the regex from ^(.+)\\1$ to ^(.+)\\1+$ to allow any number of repeated matches (not just one):

input |> 
  with(map2(start, end, seq)) |> 
  unlist() |> 
  keep(\(x) str_detect(x, "^(.+)\\1+$")) |> 
  sum()